The present invention generally relates to a liquid supply or drain pipe for a chemical process tank and more particularly, relates to a liquid supply or drain pipe for a chemical process tank that is equipped with a detector for inner leakage of liquid.
In the processing of semiconductor devices, a variety of liquid chemicals are used in processes such as cleaning, etching, photolithographic processes etc. These chemical processes are frequently conducted either in a process tank or the liquid chemical is first stored in a reservoir tank and then dispensed. In any event, the liquid chemical must first be transported into a process tank and then drained from the tank. When the chemical process is to be conducted in the process tank, i.e. such as in a wet etch process, the liquid chemical in the tank must also be replaced or replenished after repeated usage, i.e. by draining from the tank through a drain pipe into a waste chemical collection tank.
A conventional liquid chemical process tank equipped with a supply conduit and a drain conduit is shown in FIG. 1. The liquid chemical process system 10 consists of a process tank 12, a supply conduit 14 and a drain conduit 16. The process tank 12 is shown equipped with an optional overflow tank 18 for receiving an overflow of liquid chemical 20 from the process tank 12. The supply conduit 14 consists of a first supply pipe 22, a supply valve 24 and a second supply pipe 26. The supply valve 24 utilized is a normal-closed type which opens only when activated. The drain pipe 16 consists of a drain valve 28, a first drain pipe 30 and a second drain pipe 32. The overflow tank 18 is further equipped with a recycling pipe 34 for recycling overflow liquid chemical 20 through pump 36, the first drain pipe 30 and a filter 38 back into the process tank 12.
The conventional liquid chemical process system 10 has several operational drawbacks. First, when there is an internal leakage in the supply valve 24 when the valve is supposed to be closed (i.e. in a normal-closed position when not activated), liquid chemical continuously flows into the process tank 12 through the second supply pipe 26. The terminology of xe2x80x9cinner leakagexe2x80x9d is used to denote a situation wherein liquid leaks through an internal passageway, i.e. through the supply valve 24, and therefore cannot be detected by leakage detectors that are frequently mounted outside the process tank 12 for detecting leakage from the tank or from the supply pipes 22,26. The inner leakage through the supply valve 24, therefore, cannot be detected by this type of leakage detectors. As a result, the inner leakage cannot be detected by machine operators when liquid chemical continuously flows into the process tank 12, and thus making the concentration of the process chemical out of control. Since most semiconductor processes require an accurate control of the composition of the process chemicals, any deviation from the specified chemical composition renders the process unreliable and the product made by the process out of control.
A typical processing problem caused by out-of-specification chemical concentrations is shown in FIG. 2 of a chemical wet etch system. The etch rates are plotted against the number of days the etch chemical has been used illustrating a gradual decrease in the etch rates due to a continuous dilution (or decrease in concentration) of the liquid chemical in the process tank.
Similar processing problems can also be caused by the lack of detection of a leakage in the drain conduit 16, shown in FIG. 1. When the drain valve 28, of the normal-closed type, fails to close completely, liquid chemical 20 in the process tank 12 continuously drains away through drain conduit 16 into a waste collection tank (not shown). This causes excessive usage of the liquid chemical. The inner leakage of liquid chemical through the drain valve 28 cannot be detected by conventional leakage detectors that are mounted in the liquid process system 10.
An example of excessive usage of a liquid chemical is when an inner leakage is not detected as shown in FIG. 3. When the inner leakage is finally corrected in August, the usage of liquid chemical returns to a normal volume.
In accordance with the present invention, a liquid supply or drain conduit system that is equipped with an inner leakage detector is provided. In an alternate embodiment, a liquid process tank that is equipped with a liquid supply/drain system capable of detecting an inner leakage is further provided.
In a preferred embodiment, a liquid supply or drain conduit system equipped with an inner leakage detector is provided which includes a first conduit for feeding a liquid into an inlet of a first valve of the normal-closed type, a second conduit of T-shape having a horizontal portion and a vertical portion, the horizontal portion of the second conduit flows the liquid from an outlet of the first valve into a reservoir tank, a second valve of the normal-open type that has an inlet and an outlet, the inlet is situated in relation to the first valve in such a way that it receives through a vertical portion of the second conduit a leaked flow of liquid by gravity when the normal-closed first valve failed to close, and a leakage detector for detecting a flow of liquid through the second valve.
In the liquid supply or drain pipe equipped with a leakage detector, the reservoir tank may be a chemical process tank, or a waste chemical collection tank. The leakage detector may further include a liquid flow meter, or an alarm to be activated when a liquid flows through the second valve. The leakage detector sends a signal to a micro-processor when a flow of liquid through the second valve is detected. The leakage detector further sends a signal to a close-loop control system for closing the first valve when a flow of liquid through the second valve is detected.
The present invention is further directed to a liquid process tank that is equipped with a supply/drain system capable of detecting inner leakage that includes a process tank for receiving a fresh liquid from a second conduit and for draining a used liquid to a third conduit, a first conduit for feeding the fresh liquid into an inlet of a first valve of the normal-closed type, the second conduit is provided in a T-shape that has a horizontal portion and a vertical portion, the horizontal portion flows the fresh liquid from an outlet of the first valve into the process tank, a second valve of the normal-open type that has an inlet and an outlet, the inlet is situated in relation to the first valve in such a way that it receives through the vertical portion of the second conduit a leaked flow of the fresh liquid by gravity when the first valve failed to close, a first leakage detector for detecting a flow of the fresh liquid through the second valve, the third conduit for draining the used liquid from the process tank into an inlet of a third valve, a fourth conduit that is provided in a T-shape that has a horizontal portion and a vertical portion, the horizontal portion receives the used liquid from an outlet of the third valve and delivers the used liquid to a used liquid collection tank, a fourth valve of the normal-closed type that has an inlet and an outlet, the inlet is situated in relation to the third valve in such a way that it receives through the vertical portion of the fourth conduit a leaked flow of the used liquid by gravity when the third valve failed to close, and a second leakage detector for detecting a flow of the used liquid through the fourth valve.
The liquid process tank that is equipped with a supply/drain system capable of detecting inner leakage may further include a micro-processor for receiving a signal from the first and the second leakage detector when a leakage is detected by either one of the detectors. The liquid process tank may further include an alarm system to be activated by a signal received from either one of the first or the second leakage detectors. The process tank may be an etch tank, or a photoresist liquid reservoir tank. The process tank may further include an outer overflow tank for receiving overflow from the process tank. The process tank may further include an outer overflow tank and a pump for pumping an overflow from the process tank back into the process tank. The first valve may be a supply valve and the third valve may be a drain valve. The first and the second leakage detectors may further include a liquid flow meter for sensing a flow of liquid therethrough.
It is therefore an object of the present invention to provide a liquid supply or drain conduit system that does not have the drawbacks or shortcomings of the conventional liquid supply or drain systems.
It is another object of the present invention to provide a liquid supply or drain conduit system that is equipped with an inner leakage detector.
It is a further object of the present invention to provide a liquid supply or drain conduit system that is provided with at least one valve module for detecting an inner leakage.
It is another further object of the present invention to provide a liquid supply or drain conduit system wherein a supply valve or a drain valve is further equipped with a normal-open valve and a leakage detector.
It is still another object of the present invention to provide a liquid supply or drain conduit system equipped with an inner leak detector such that an alarm is activated when a leakage is detected.
It is yet another object of the present invention to provide a liquid process tank that is equipped with a supply/drain system capable of detecting an inner leakage of a liquid chemical.
It is still another further object of the present invention to provide a liquid process tank that is equipped with a supply/drain system capable of detecting an inner leakage of fresh chemical from the supply conduit or an inner leakage of used chemical from the drain conduit.